javengar
Structural
- Sep 12, 2024
- 2
Hi, I'm a rockie engineer from Latin America. I'm kind of confused with the shear demands I should use to analyze lateral demands in pile caps.
I have this ten story building with a basement story modeled on CSI ETABS. The model is base fixed. The base shear is around 1000 tons. Since I live in a high seismic area with soft soils, I will have to use pile foundation. Piles reinforcement would be design according to the shear and moment demands of a pile lateral analysis. But, I have a problem with the shear reactions of my model on ETABS.
These are the shear reactions on "X" direcction of my model considering a static seismic analysis on the positive "X" direcction. As you can see, the demands on the wall are in one directions and the others are on the opposite direcction. If a sum these demands on the walls the result is 1800 tons, and the sum of the other reactions is -800 tons, giving a total sum (actual subtraction) of 1800 tons - 800 tons = 1000 tons (equivalent to the base shear) Why is this happening? Some kind of shear reveral effect on the interior columns? Some kind of backstay effect? Eventhough I don't have interior shear walls and the building area is equivalent to the basement area. Should I use these shear demands to do the pile lateral analysis? It is better to estimate the lateral stiffness (springs) of pile groups to capture the lateral demand distribution since during a seismic event, all pile groups would deflect to the same direction since they will be tied by tie beams and a basement thick slab?
Thank you in advance for your answers.
Note 1: I'm not really in charge to analyze this building, I'm just curios about this effect that I've seen in buildings modeled with basement stories and fixed base.
I have this ten story building with a basement story modeled on CSI ETABS. The model is base fixed. The base shear is around 1000 tons. Since I live in a high seismic area with soft soils, I will have to use pile foundation. Piles reinforcement would be design according to the shear and moment demands of a pile lateral analysis. But, I have a problem with the shear reactions of my model on ETABS.
These are the shear reactions on "X" direcction of my model considering a static seismic analysis on the positive "X" direcction. As you can see, the demands on the wall are in one directions and the others are on the opposite direcction. If a sum these demands on the walls the result is 1800 tons, and the sum of the other reactions is -800 tons, giving a total sum (actual subtraction) of 1800 tons - 800 tons = 1000 tons (equivalent to the base shear) Why is this happening? Some kind of shear reveral effect on the interior columns? Some kind of backstay effect? Eventhough I don't have interior shear walls and the building area is equivalent to the basement area. Should I use these shear demands to do the pile lateral analysis? It is better to estimate the lateral stiffness (springs) of pile groups to capture the lateral demand distribution since during a seismic event, all pile groups would deflect to the same direction since they will be tied by tie beams and a basement thick slab?
Thank you in advance for your answers.
Note 1: I'm not really in charge to analyze this building, I'm just curios about this effect that I've seen in buildings modeled with basement stories and fixed base.